Conventionally, when an image is projected by a projecting device such as a projector onto a screen, the projected image may be distorted in a trapezoidal shape (trapezoidal distortion) depending on a relative positional relationship between the projecting device and the screen. Further, a projected image may be non-linearly distorted due to local concavity and convexity or distortion of the screen surface.
To correct such distortion, there has been a known technique in which, an image of a screen, on which an image pattern that includes arranged specific figures is projected, is captured by a digital camera, a distortion level is calculated based on a difference between a position of a feature point extracted from the actually captured image and the corresponding ideal position of the feature point, and the image is corrected by correcting the distortion.
As an example of such a conventional technique, Patent Document 1 discloses an image correction device in which a pattern including feature points arranged at equal intervals (a feature-point pattern) is projected on a screen and captured, a distortion amount due to the projection is calculated by using the coordinates of the feature points included in the captured image, and the projected image is corrected based on the calculated distortion amount.